What is orderer role in hyperledger? and from where?

Hi, it confused me that where does orderer resources from? Peers are from different organizations, and I thought that orderers are also from different organizations, but can't find any doc about this, can any one give some help?

I thought that an organization will provide some orderers and some peers, right?

It is important when trying to understand MSP of orderers. Currently, org of orderers are standalone, I don't understand why designed in this way. is there any background?